....maybe we are too smart for our own good anyways, so killing a few brain cells is a good thing. 
I believe either you are "smart" or you are not. Some of the dumbest, knuckle dragging, mouth breathing people I know are not cannabis users. By contrast, some of the most intelligent/educated people I know are regular users.
Now I'm not saying pot makes you smart. It does not. But it does certainly not "make you stupid." Yeah, smoking a pound a day is probably not a great idea for your brain, lungs, and so on. But a few tokes here and there is no more harmful than anything else that is "bad for you." Deep fried food, movie popcorn, getting hammered off booze, stress, all you can eat sushi, and so on.
It just another way to unwind/relax. Yeah it would be better if you didn't touch the stuff, or drink, or eat Mcdonalds - but common live a little! If you like the stuff then friggen buy some and enjoy it. If you don't like the effects then that's fine too, but don't talk down to those who enjoy cannibas unless you can honestly say you yourself do not make any "unhealthy choices."